The overall objective of this research project is to determine how various presynaptic factors control the magnitude and time course of neurotransmitter release from presynaptic motor nerve terminals during repetitive nerve stimulation. Stimulation of presynaptic nerve terminals is followed by (1) a brief burst of transmitter release which produces the end-plate potential, and (2) a prolonged period of elevated release probability manifested as as increased frequency of "spontaneous" miniature end-plate potentials (delayed release) and as an increase in the end-plant potentials evoked by subsequent nerve stimulation (facilitation). A major current model of the transmitter release mechanism says that delayed release and facilitation are both caused by an elevated calcium concentration inside the nerve terminal. The proposed experiments will test this model by measuring delayed release and facilitation simultaneously under a variety of experimental conditions. The results of this study will help us understand how past activity changes the efficiency of interneuronal communication. BIBLIOGRAPHIC REFERENCES: E.F. Barrett & K.L Magleby (1976). "Physiology of Cholinergic Transmission" in Biology of Cholinergic Function, eds. A.M. Goldberg & I. Hanin. Raven Press, New York. E.F. Barrett & J.N. Barrett (1976). Separation of two voltage sensitive potassium currents, and demonstration of a tetrodotoxin - resistant calcium current in frog mononeurones. J. Physiol. (Lond.) 255. 737-744.